This invention relates generally to a ballast scheme for operating multiple lamps and, more particularly, to a ballast scheme for operating multiple fluorescent lamps having substantially the same current flowing through each lamp.
Conventional ballasts for powering multiple lamps, such as disclosed in U.S. Pat. No. 4,293,799, include a plurality of transformers for isolating the lamps from direct connection to a utility line. The primary windings of the transformers are connected in series. The secondary winding of each transformer is connected to a lamp. Substantially the same current flows through each lamp when the lamps have substantially the same impedance.
Such conventional ballasts, however, often do not sense lamp load conditions so as to achieve/maintain one or more desired lamp parameters. These parameters can include, but are not limited to, the level of illumination, power regulation, preheat, ignition stop/cutoff and/or capacitive mode protection.
It is therefore desirable to provide an improved ballast for operating multiple lamps in which substantially the same level of current flows through each lamp. The improved ballast should include a scheme for sensing lamp load conditions in order to achieve/maintain one or more desired lamp parameters. The scheme should avoid the use of expensive components and minimize the number of components required.